The present invention relates generally to fastener driving tools used for driving fasteners into workpieces to secure materials to the workpieces (referred to as workpiece materials), and specifically to fastener driving tools configured for driving two-legged fasteners, one example of such being referred to as a staple.
Conventional fastener driving tools feature a reciprocating driver blade which impacts a fastener fed to a nosepiece by a magazine. Whether powered pneumatically, manually, by combustion or electricity, such tools provide sufficient force to the driver blade that it separates the fastener from adjacent fasteners in the magazine, and drives the fastener so that the fastener is sufficiently embedded in the workpiece.
Commercially available two-legged fasteners include a pair of separated, generally parallel legs separated by a crown to form an inverted “U”-shape. Such fasteners are typically used in the installation of workpiece materials such as asphalt roofing shingles, building siding, wallboard, Romex® wire, Nomex® wire, Tyvek® insulation wrap, other insulation felts and other similar applications. One operational problem of two-legged fasteners is that the legs are sometimes driven too deeply into the workpiece, causing the crown to pierce the surface of the workpiece material. When this happens, the workpiece material is not as securely held. In other words, the amount of force needed to pull the workpiece material away from the workpiece (“pull through”) decreases when the workpiece material has been pierced. A side effect of this piercing is that the workpiece material may be damaged.
Another drawback of currently available two-legged fasteners has resulted in an effort to increase the clamping force provided. In some cases, workpiece material secured to a substrate by two-legged fasteners can become detached if the material is exposed to certain forces, including high winds.
Still another design consideration of such two-legged fasteners is that if relatively delicate workpiece materials are intended for installation, including the cable or wire products described above, the crown portion of the fastener may damage the cable or other material.